【作者】 杨延强；

【导师】 易维明；

【作者基本信息】 沈阳农业大学 ， 农业生物环境与能源工程， 2011， 博士

【摘要】 生物质快速热裂解液化技术是国际上流行的一种生物质废弃物处理和利用技术。下降管式裂解液化装置是国内具有自主知识产权的生物质快速热解液化反应器。在高的升温速率下,生物质在反应管中迅速热裂解为生物质半焦(残炭),因此实质上反应管内是生物质半焦与陶瓷球混合颗粒的换热。在下降管内,生物质的热裂解不仅受热裂解动力学控制,而且还要受到颗粒的流动与传热过程影响,因此要研究下降管反应器内生物质的热裂解规律,必须对颗粒的流动规律进行研究。本文从实验、理论分析和数值模拟三方面入手对陶瓷球颗粒与生物质半焦粉体颗粒在45°倾斜下降管反应器内的混合流动规律进行了深入的研究。从而揭示下降管反应器内混合颗粒的运动机理,以在理论上指导、优化装置的参数设计,进而提高系统效率。设计了45°倾斜下降管颗粒流动冷态实验装置,对实验装置的喂料系统进行了实验研究,结果表明喂料量与喂料时间成线性关系,能够满足实验需要。同时建立了移动误差小于1mm的相机自动控制系统,使实验更加精确、方便和快捷。对于PIV系统来说,横截面为方形的管道要比圆形管道测试效果好,为此本文对横截面为方形、半圆半方和圆形三种不同管道进行了对比实验,结果表明在倾斜下降管冷态实验中,不能用方管或半圆半方管来代替圆管进行实验。利用“插板法”对倾斜下降管中混合颗粒的浓度分布规律进行了研究,分别获得了陶瓷球颗粒与生物质半焦粉体颗粒的浓度分布规律,为颗粒碰撞模型中的浓度分布参数n的确定提供数据支持。利用与PTV相结合的“粒径分析法”、与PIV相结合的“速度方向判别法”和Sommerfeld和Oesterle提出的随机颗粒碰撞理论模型对下降管中陶瓷球颗粒碰撞率f进行了研究,根据实验值对随机颗粒碰撞模型进行了修正。碰撞率的获得可直接计算出生物质热裂解中由碰撞直接传递的热量f·Q。利用荧光技术与PIV技术相结合的方法在距入口690mm和1190mm截面上对混合颗粒中陶瓷球颗粒的速度进行了测试,并获得了陶瓷球的速度,证明了此方法的可行性。通过对生物质半焦粉体颗粒速度分布规律研究发现,其轴向时均速度分布在整个管道内分为三部分,开始段的流体控制阶段、颗粒/流体协调控制的过渡段和稳定后的颗粒控制阶段；径向时均速度变化不大。流体控制阶段的生物质半焦轴向时均速度分布与气体射流分布类似,最大速度在管道中心,随着下降距离的增大,颗粒在管道中的作用越来越明显,最大速度位置下移,向管道底部迁移,最后稳定在大约管底(y/d=0.2)附近；在颗粒控制阶段的管道截面上,从管顶到管底同样分为三部分：靠近管顶(y/d=0.9-1)的属于“牛顿流体”的粘性底层,中间部分(y/d=0.1-0.9)和靠近管底(y/d=0～0.1)的“柱塞流”。陶瓷球和生物质半焦速度分布规律的研究得出下降管“Z”字形直管道长度在590mm范围内更加有利于换热。对生物质半焦颗粒停留时间研究发现,其受抽气量影响最大,陶瓷球粒径次之,基本不受混和质量比例的影响。颗粒停留时间的研究为管道总长度的设计提供数据支持。根据倾斜下降管中生物质半焦和陶瓷球混合颗粒的流动现象及其运动规律,建立了描述下降管反应器颗粒混合流动规律的拉格朗日和欧拉总数学模型,并利用Fluent软件进行了数值模拟。在距入口90mm的截面上,实验和模拟的轴向时均速度分布符合较好；在距入口1190mm截面上,由于饱和夹带量的高估,使得实验和模拟的轴向时均速度分布符合较差。更多还原

【Abstract】 Fast biomass pyrolysis is a popular international technology to process and utilize the biomass waste. The down flow tube reactor heated by ceramic balls solid heat carrier is a new type reactor for biomass pyrolysis and it has been patented in China. In a high heating rate, biomass becomes biomass-char (residual carbon) by fast pyrolysis, so the heat transfer occurs between the biomass-chars and ceramic balls in the reaction tube.In the down flow tube reactor, biomass pyrolysis is controlled not only by pyrolysis kinetics but also by the particle flow and heat transfer, so to study the law of biomass pyrolysis in the down flow tube reactor, it must be study the law of particle flow.The paper studied the principles of ceramic balls and biomass-char particles mixed flow behavior through experiments, theoretical analysis and numerical simulation in the 45°inclined down flow tube reactor, and revealed the movement mechanism of mixed granular. These studies would contribute to the design and increase system efficiency.In this paper, a 45°inclined down flow tube reactor cold experimental apparatus was designed, and the feeding system of the experimental devices were experimentally investigated, results show that the volume of feed and feeding time into a linear relationship, to satisfy the experimental needs. While establishing a camera automatic control system with mobile error of less than 1mm that makes the experiments more precise, convenient and fast.For the PIV system, the test results of a pipe with square cross-section are better than a circular pipe. So in this paper, a square, semicircle and a semi circular-square channels were tested and the results showed that a square or semi circular-square tubes could not take place of a circular tube to do experiments in the down flow tube reactor.It studies the concentration distribution of mixed particles by the "flapper method" in the inclined down flow tube reactor, and obtains the concentration distribution of ceramic ball and biomass-chars particles. It provides data to support the determination of concentration distribution n in the particle collision model.Ceramic balls collision rate is studied by PTV combined with the "particle size analysis," PIV combined with the "direction of velocity discrimination law" and theoretical model of random collisions of particles of Sommerfeld and Oesterle proposed in the down flow tube reactor, and amend the random particle collision model according to the experimental values. Collision can calculate the heat transfer f·Q by the collision in biomass pyrolysis.Using fluorescence technique measured the velocity of ceramic balls in the cross-section of 690mm and 1190mm away from entrance and received the speeds, it proves the feasibility of this method.Axial mean velocity distribution of biomass-char were divided into three parts in the entire pipeline, the beginning section of the fluid control, transition section of particle/fluid control and the stable section of the particle control; radial mean velocity changed little.In the fluid control section, the axial mean velocity distribution of biomass-char is similar to the jet gas, the maximum speed in the center of the tube; with the decline in the distance increases, the role of particles in the pipe more and more obvious, the maximum speed position down, move to the bottom of the pipe, and finally stabilized at around the bottom of the tube (y/d=0.2); In the pipe cross-section of the particle control section, from the top to the bottom of the tube is also divided into three parts:near the top tube (y/d=0.9～1) is the viscous sublayer of "Newtonian fluid", the middle part (y／d=0.1～0.9) and close to the bottom of the tube (y/d=0～0.1) is the "plug flow."Studies of the ceramic balls and biomass-char velocity distribution show that the straight pipe length 590mm range is more conductive to heat.Residence time of biomass-char granular is affected most by the amount of exhaust, followed by the ceramic particle size, and largely unaffected by the mixed mass ratio. Studies of particle residence time provide data to support the design of the total length of the pipe.According to the flow phenomena and motion laws of ceramic ball and biomass-char in inclined down flow tube reactor, established general mathematical model of Lagrange and Euler to describe the mixed particles flow laws of the down flow tube reactor. Using Fluent to simulate flow laws of ceramic ball and biomass-char in inclined down flow tube reactor.At the cross-section of 90mm away from entrance, the axial mean averaged velocity distribution of the experimental is closer to the simulated; at the cross-section of 1190mm away from entrance, due to the amount of saturation entrainment is overestimated, making large differences between the experimental and simulated axial mean velocity distribution.更多还原